Rose-scented geranium (Pelargonium species) is a shrubby, herbaceous, perennial plant that belongs to the Geraniaceae family. In South African rural communities, the Pelargonium species are known for their use in herbal medicine (Lis-Balchin, 2002). However, at a commercial level, the rose-scented geranium is cultivated for its essential oil, which is produced in glands (trichomes) throughout the green parts of the plant, mainly on the leaves (Rhind, 2012). Rose-scented geranium essential oil is an important component of the different products used in the perfumery, aromatherapy, pharmaceutical, and food-processing industries (Prins et al., 2010; Singh, 1999).
Rose-scented geranium essential oil is composed of more than 120 compounds that belong to different organic compound classes, acids, alcohols, aldehydes, esters, and ketones (Demarne and Van der Walt, 1993; Williams and Harborne, 2002). The major constituents of the oil are citronellol, geraniol, iso-metone, citronellyl formate, and geraniol formate (Peterson et al., 2006; Weiss, 1997). Market value of rose-scented geranium essential oil is determined by composition (the proportion of the compounds, mainly the citronellol-to-geraniol ratio) and the quantity supplied.
Today the demand for geranium oil worldwide is estimated to be around 600 tons per year (Eiasu, 2009; Shawl et al., 2006). About 20–25 tons of geranium oil are required to close the world’s demand for essential oil (Demarne, 2002; Eiasu, 2009). According to Schwab et al. (2008), the international trade of essential oil increases annually on average by 10% a year.
It is well documented that plant developmental stages as well as leaf ages have a strong effect on the volatile composition of aromatic plants. For instance, in sage (Salvia officinalis), higher camphor content was found on young growing leaves (Croteau et al., 1981). Havkin-Frenkel and Belanger (2008) also concluded that there are dramatic differences among the leaves of the same plant, depending on their age and position. According to the authors, the lower leaves contain a lower concentration of volatiles compared with the upper, younger leaves—and also their composition differs. Singh et al. (1989) confirms that young, expanding leaves are biogenetically more active than mature leaves. Furthermore, an experiment on peppermint showed that there is little de novo synthesis of monoterpenes from 14 CO2 in mature leaves, and more in immature leaves that are still expanding (Croteau et al., 1981). Research on Cistus ladanifer showed that young leaves produce more flavonoids and diterpenes (Masa et al., 2016). Thus, leaf age is an important factor affecting essential oil content and composition.
Information on essential oil yield and composition as affected by leaf age and position in rose-scented geranium is limited. Literature does reveal that essential oil and composition depend on the shoot age of aromatic plants (Motsa et al., 2006). Therefore, an investigation into leaf age (position) would help rose-scented geranium producers to develop efficient harvesting cycles. Hence, the main objective of the current research was to examine rose-scented geranium oil yield and quality as affected by leaf age and position. We aimed to quantify the contribution of each leaf age group.
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